34. Genetic Code and RNA

We briefly reviewed the Beadle and Tatum results indicating that genes encode polypeptides, then moved on to discuss how the order of amino acids in a polypeptide chain is specified by the sequence of bases making up RNA. This sequence is “read” 3 bases at a time, which is called a codon, which specifies a particular amino acid.

Slides: Transcription and Genetic Code

31. DNA Function and Structure

We looked at the 3 key experiments in the history of biology that pointed to DNA as the hereditary material, including the Griffith transformation experiment, followed up by Avery, MacCleod, and McCarty, and finally the Hershey and Chase experiment. Then we turned to the structure of DNA and how it encodes information.

Slides: DNA Function and Structure

28. Mendel & Inheritance

An introduction to the key ideas and insights gained as Mendel studied the inheritance of 7 characteristics of garden peas. He collected large quantities of data by scoring the phenotypes of offspring from carefully controlled cross-pollination events, using inductive reasoning to arrive at a set of principles of inheritance that we still largely accept today.

Slides: Mendel & Inheritance

27. Meiosis

Meiosis is the special form of nuclear division that cuts the ploidy level (number of versions of chromosomes) in half. This is the process that enables sexual reproduction to occur by maintaining the same ploidy level afer fertilization as before meiosis. Meiosis is made up of 2 rounds of division with no intervening synthesis phase, and includes a special process during the first round in which homologous chromosomes pair up.

Slides: Meiosis